Hanna Mustaparta

Chemical communication in heliothine moths

Abstract1.Projection patterns of olfactory receptor neurons, specifically tuned to the two principal components of the female H. virescens sex pheromone blend, and to a third pheromone-like compound of possible antagonistic significance, were examined using a combined electrophysiological and morphological technique.2.The macroglomerular complex consists of four major glomerular subdivisions.3.In the sensillum type containing a receptor neuron detecting the main pheromone component, Z11-16: AL, two cells were present. When the sensillum was stimulated with Z11-16:AL, a single axon, stained by a method that selectively stains active neurons, was seen projecting into the large a glomerulus. The b glomerulus was innervated by a second neuron in a few double stainings.4.In a second sensillum type, one receptor neuron tuned to the second major pheromone component, Z9-14:AL, was found. In these sensilla, one or two receptor neurons of unknown specificity were also observed. When the sensillum was stimulated with Z9-14: AL, a single neuron projecting into glomerulus a or two neurons projecting into glomerulus a were most often observed.5.In the third sensillum type, one neuron specifically tuned to Z11-16:AC projected to glomerulus c, and a second cell of unknown specificity projected to the same area.6.The axonal arborizations of different physiological receptor neuron types involved in the detection of the pheromone blend do not display a clearcut morphological separation into different glomeruli in the MGC. A separation between neurons detecting attracting and repelling odours was, however, present.

The macroglomerular complex of the antennal lobe in the tobacco budworm moth Heliothis virescens : specified subdivision in four compartments according to information about biologically significant compounds

Abstract The functional organisation of the male specific macroglomerular complex in Heliothis virescens has been studied by tip recordings of sensilla trichodea type 1 combined with cobalt-lysine stainings and by intracellular recordings of antennal lobe projection neurons combined with neurobiotin stainings. The antennal lobe, the macroglomerular complex and the stained axons/dendrites were reconstructed by camera-lucida. Some were further computer reconstructed in three dimensions. The results showed that: 1) The macroglomerular complex consisted of four anatomically separated compartments; 2) A large compartment (the cumulus) at the entrance of the antennal nerve received input from receptor neurons responding to the major pheromone component; 3) Another large compartment, located dorso-medially of the cumulus (the dorso-medial compartment) received input from receptor neurons tuned to the second pheromone component; 4) Two ventrally located compartments received input from two receptor neuron types, co-localized in the same sensillum. Each neuron type responded strongest to one of two interspecifically acting signals, shown to interrupt the pheromone attraction. 5) The function of the dorso-medial compartment was further verified by selective arborizations in this compartment by a projection neuron showing strong response to antennal stimulation with the second pheromone component. At low concentration, the neuron responded synergistically to stimulation with the binary pheromone mixture.

Digital Atlases of the Antennal Lobe in Two Species of Tobacco Budworm Moths, the Oriental Helicoverpa assulta (Male) and the American Heliothis virescens (Male and Female)

The antennal lobe of the moth brain is the primary olfactory center processing information about pheromones and plant odors. We present here a digital atlas of the glomerular antennal lobe structures in the male of Helicoverpa assulta and the male and female of Heliothis virescens, based on synaptic antibody staining combined with confocal microscopy. The numbers of the glomeruli in the three specimens were similar, 65, 66, and 62, respectively. Whereas the male antennal lobe has a macroglomerular complex consisting of three and four units in the two species, the female lobe has two enlarged glomeruli at a corresponding position, near the entrance of the antennal nerve. Another large glomerulus, showing homology in the three specimens, is ventrally located. The small size of the heliothine moths is advantageous for confocal microscopy because the entire brain can be visualized as a single image stack. The maps are freely accessible on the internet, and the digital form of the data allows each atlas to be rotated and sectioned at any angle, providing for the identification of glomeruli in different preparations. J. Comp. Neurol. 446:123–134, 2002.

Chemical communication in heliothine moths. II : Central processing of intra- and interspecific olfactory messages in the male corn earworm moth Helicoverpa zea

Summary1.The antennal lobes (ALs) in the brain of the corn earworm moth Helicoverpa zea (formerly Heliothis zea; Lepidoptera: Noctuidae) were examined using combined anatomical and electrophysiological methods. Like other moths, male H. zea possess a sex-specific macroglomerular complex (MGC) for processing information about the female sex-pheromone blend. Unlike other moths, however, the MGC in H. zea consists of 3 distinct glomerular structures: two situated dorsally, and a third situated ventrally (Fig. 1).2.Intracellular recording and staining revealed a population of projection neurons that link the MGC with the protocerebrum (Figs. 4, 7, and 11). Four physiological classes of MGC neurons were identified based upon their responses to stimulation of the antenna with different components of the pheromonal blends of H. zea and Heliothis virescens (a sympatric species). One class responded selectively to the principal component in both species, Z11 16:AL (Figs. 2 and 3). A second, more broadly tuned class showed strong responses to Z11-16:AL and also to other pheromonal components (Figs. 5 and 6). A third class did not respond to Z11-16:AL but did respond to Z9-14:AL, a substance released by H. virescens females that helps attract conspecific males while it inhibits the attraction of H. zea males (Figs. 8, 9 and 10). Some of these neurons also responded to another pheromonal component required for male attraction in H. zea, Z9-16: AL. A fourth class responded in a unique fashion to a blend of Z11-16: AL and Z9-14:AL(Fig. 12).3.Projection neurons that responded to Z11-16:AL had arborizations in all 3 MGC glomeruli (Figs. 4 and 7), whereas neurons that responded to Z9-14:AL from H. virescens had arborizations in just one of the dorsal glomeruli of the MGC (Fig. 11). Thus these two types of neurons with widely different quality-coding functions have overlapping arborizations in one dorsal glomerulus in the MGC, demonstrating that the MGC is not exclusively involved with processing species-specific (pheromonal) information.

Fine structure of antennal sensilla basiconica and their detection of plant volatiles in the eucalyptus woodborer, Phoracantha semipunctata Fabricius (Coleoptera: Cerambycidae)

The ultrastructure and distribution pattern of two types of basiconic sensilla (I and II) on the antennal flagellum of both sexes of Phoracantha semipunctata (Coleoptera: Cerambycidae) was investigated by scanning and transmission electron microscope. Both types are thin-walled multiporous sensilla and occur mostly along the anterior border of the Fl1-Fl6 flagellomeres, while on the distal flagellomeres (Fl7-Fl9) they are more evenly distributed on both surfaces. Clusters of sensilla basiconica II are found on the distal half of the anterior border of the Fl1-Fl6 flagellomeres. Sensilla basiconica I have one bipolar sensory cell with a branched distal dendrite, whereas the sensilla basiconica II contain two bipolar sensory cells with branched distal dendrites. No sexual dimorphism was found in the fine structure and distribution pattern of both types of sensilla basiconica. Responses from single sensory cells to host and non-host plant odors were examined, using gas chromatography linked with electrophysiological recordings. Most cells associated with each sensillum type were narrowly tuned, each specialized for the detection of one or two chemically related compounds. No clear functional distinction between the two morphological types of sensilla was found, although the few cells that responded specifically to non-host volatiles were associated with sensilla basiconica II.

Heliothis virescens: Response characteristics of receptor neurons in Sensilla Trichodea type 1 and type 2

Partial electroantennograms (EAGs) and single cell recordings fromHeliothis virescens males have demonstrated the presence of pheromones receptor neurons in sensilla trichodea type 2 as well as in type 1. This is supported by cobalt tracing experiments, showing that primary axons from the distal flagellum, containing only s. trichodea type 2, project into the macrogiomerulus complex in the male antennal lobes. Four types of finely tuned pheromone receptor neurons were found in males, whereas in females the corresponding neurons responded mainly to host odors. In males the majority (75 and 18%, respectively) were tuned to the majorHeliothis virescens pheromone components (Z)-11-hexadecenal (Z11-16∶A1) and (Z)-9-tetradecenal (Z9-14∶A1). The others (5 and 2%, respectively) responded specifically to (Z)-1 1-hexadecen-1-ol (Z1 1-16∶OH) and (Z)-1 1-hexadecen-1-ol acetate (Z1 1-16∶Ac). No neurons responding selectively to the minor pheromone components were found. The Z11-16∶A1 neurons of both sensilla types possessed similar specificity. However, the sensitivity decreased toward the medial and distal part of the flagellum, where s. trichodea type 2 are located. This suggests that the pheromone concentrations can be detected peripherally by a spatial as well as a temporal mechanism. Differences in temporal response patterns (pronounced phasic vs. tonic component) were found within the same type of neurons, suggesting different ability to encode intermittency of the pheromone plume as well as to mediate maintenance of flight.

Enantiomeric Composition of Monoterpene Hydrocarbons in Some Conifers and Receptor Neuron Discrimination of α-Pinene and Limonene Enantiomers in the Pine Weevil, Hylobius abietis

The enantiomeric composition of seven monoterpene hydrocarbons in headspace volatiles of spruce sawdust and seedlings (Picea abies), pine seedlings (Pinus sylvestris), and branches of juniper (Juniperus communis) was determined by gas chromatographic separation on a β-Cyclodextrin column. For the six monoterpenes, α-pinene, camphene, β-pinene, sabinene, limonene, and β-phellandrene, both enantiomers were present, whereas for 3-carene only the (+)-configuration was found. The amount of each enantiomer varied considerably both in relation to total amount of all of them, and for the six pairs also in relation to the opposite enantiomer. One olfactory receptor neuron in the pine weevil (Hylobius abietis) showed a strong response to α-pinene when stimulated with all four headspace materials via a GC equipped with a DB-WAX column. The same neuron was subsequently tested with repeated stimulations via the GC effluent containing the (+)- or (–)-enantiomer. A marked better response to (+)- than to (–)-α-pinene was elicited. Another olfactory receptor neuron that responded strongly to limonene when stimulated with the spruce volatiles was tested for enantiomers of limonene. This neuron responded more strongly to (–)- than to (+)-limonene, when stimulated alternately with each of the limonene enantiomers. Discrimination between enantiomers by plant olfactory receptor neurons suggests that the enantiomeric ratios of volatile compounds may be important in host location by the pine weevil.

Chemical communication in heliothine moths - VI. Parallel pathways for information processing in the macroglomerular complex of the male tobacco budworm moth Heliothis virescens

The chemical and temporal features of the sex-pheromone emitted by Heliothis virescens females are encoded by a diverse array of output pathways from the male-specific macroglomerular complex (MGC) in the antennal lobe. Most output neurons (29 out of 32) were activated by antennal stimulation with the principal component of the sex-pheromone blend of this species, (Z)-11-hexadecenal. Six neurons were excited solely by this component, 8 neurons also responded to the second essential blend component, (Z)-9-tetradecenal, and 14 neurons displayed equivalent responses to the two. Many neurons also effectively encoded the onset and duration of the stimulus. In one additional neuron, a prolonged excitatory response (synergism) was evoked only by the blend of the two components, indicating that some MGC neurons function as ‘blend detectors’.In contrast to the situation in Helicoverpa zea, none of the MGC neurons in H. virescens responded selectively to (Z)-9-tetradecenal, suggesting that these two noctuid species employ different neural strategies to encode information about their respective pheromone blends.Three MGC-output neurons responded selectively to (Z)-11-hexadecenyl acetate, an odorant released by some sympatric species that disrupts normal upwind flight to pheromones. Thus, changes in the attractant and deterrent chemical signals, as well as the physical features of these odor plumes, are encoded in the MGC across a diverse parallel array of output pathways to the protocerebrum.

Encoding of plant odour information in insects: peripheral and central mechanisms

Insects are suitable model organisms for studying mechanisms underlying olfactory coding and olfactory learning, by their unique adaptation to host plants in which the chemical senses are essential. Recent molecular biological studies have shown that a large number of genes in insects and other organisms are coding for olfactory receptor proteins. In general, one receptor type seems to be expressed in each neurone. The functional characterisations of olfactory receptor neurones have been extensive in certain insect species, demonstrating a fine‐tuning of single neurones to biologically relevant odourants; both insect and plant produced volatiles. Stained neurones of the same functional type have been shown to project in one and the same glomerular unit in the primary olfactory centre, the antennal lobe. This corresponds to molecular biological studies, showing projections in one glomerulus by neurones expressing the same receptor type. Comparison of these findings with physiological and morphological characterisations of antennal lobe neurones has indicated correspondence between input and output of the glomerular units. Examples are presented from studies of heliothine moths. From the antennal lobe, the olfactory information is further conveyed to the mushroom bodies, particularly important for learning, and the lateral protocerebrum, a premotoric area. The three brain areas are regions of synaptic plasticity important in learning of odours, which is well studied in the honeybee but also in species of moths.

Chemical communication in heliothine moths. III : Flight behavior of male Helicoverpa zea and Heliothis virescens in response to varying ratios of intra- and interspecific sex pheromone components

Summary1.Helicoverpa zea males flew upwind and successfully contacted the source when presented with 2-component blends consisting of their principal conspecific sex pheromone component, (Z)-11-hexadecenal, plus small amounts of (Z)-9-tetradecenal, a key secondary component in the Heliothis virescens blend which has heretofore been considered antagonistic to H. zea pheromone-mediated behavior. Neurophysiological studies of H. zea antennal receptor neurons and central interneurons had suggested that this unexpected antagonistic effect on behavior might occur.2.When the amount of (Z)-9-tetradecenal in the blend reached 15% relative to the principal component its effect did become antagonistic with significantly more H. zea males remaining quiescent. Five-to-fifteen percent (Z)-9-tetradecenal is emitted by H. virescens in its pheromone blend, levels that evoked optimal upwind flight and source contact in H. virescens males.3.As suggested by studies of H. virescens antennal receptor neurons, H. virescens males were unresponsive to the reciprocal inter-specific blend, comprised of (Z)-11-hexadecenal plus various percentages of (Z)-9-hexadecenal.4.Receptors that allow such mutual replacement of compounds might permit significant shifts in pheromone systems; a single mutation that drastically alters the female sex pheromone blend could still be carried in a population due to the successful attraction of normal males by mutant females.